From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B49F1C5ACD6 for ; Wed, 18 Mar 2020 18:36:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9096420787 for ; Wed, 18 Mar 2020 18:36:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727022AbgCRSgK (ORCPT ); Wed, 18 Mar 2020 14:36:10 -0400 Received: from foss.arm.com ([217.140.110.172]:53284 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726950AbgCRSgK (ORCPT ); Wed, 18 Mar 2020 14:36:10 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id F2DA21FB; Wed, 18 Mar 2020 11:36:08 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 07E133F67D; Wed, 18 Mar 2020 11:36:05 -0700 (PDT) Date: Wed, 18 Mar 2020 18:36:03 +0000 From: Catalin Marinas To: Vincenzo Frascino Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, linux-mips@vger.kernel.org, x86@kernel.org, Will Deacon , Arnd Bergmann , Russell King , Paul Burton , Thomas Gleixner , Andy Lutomirski , Ingo Molnar , Borislav Petkov , Stephen Boyd , Mark Salyzyn , Kees Cook , Peter Collingbourne , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nick Desaulniers , Marc Zyngier , Mark Rutland , Will Deacon Subject: Re: [PATCH v4 18/26] arm64: vdso32: Replace TASK_SIZE_32 check in vgettimeofday Message-ID: <20200318183603.GF94111@arrakis.emea.arm.com> References: <20200317122220.30393-1-vincenzo.frascino@arm.com> <20200317122220.30393-19-vincenzo.frascino@arm.com> <20200317143834.GC632169@arrakis.emea.arm.com> <20200317155031.GD632169@arrakis.emea.arm.com> <83aaf9e1-0a8f-4908-577a-23766541b2ba@arm.com> <20200317174806.GE632169@arrakis.emea.arm.com> <93cfe94a-c2a3-1025-bc9c-e7c3fd891100@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <93cfe94a-c2a3-1025-bc9c-e7c3fd891100@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 18, 2020 at 04:14:26PM +0000, Vincenzo Frascino wrote: > On 3/17/20 5:48 PM, Catalin Marinas wrote: > > On Tue, Mar 17, 2020 at 04:40:48PM +0000, Vincenzo Frascino wrote: > >> On 3/17/20 3:50 PM, Catalin Marinas wrote: > >>> On Tue, Mar 17, 2020 at 03:04:01PM +0000, Vincenzo Frascino wrote: > >>>> On 3/17/20 2:38 PM, Catalin Marinas wrote: > >>>>> On Tue, Mar 17, 2020 at 12:22:12PM +0000, Vincenzo Frascino wrote: > >>>> > >>>> Can TASK_SIZE > UINTPTR_MAX on an arm64 system? > >>> > >>> TASK_SIZE yes on arm64 but not TASK_SIZE_32. I was asking about the > >>> arm32 check where TASK_SIZE < UINTPTR_MAX. How does the vdsotest return > >>> -EFAULT on arm32? Which code path causes this in the user vdso code? [...] > > So clock_gettime() on arm32 always falls back to the syscall? > > This seems not what you asked, and I think I answered accordingly. Anyway, in > the case of arm32 the error code path is handled via syscall fallback. > > Look at the code below as an example (I am using getres because I know this > email will be already too long, and I do not want to add pointless code, but the > concept is the same for gettime and the others): > > static __maybe_unused > int __cvdso_clock_getres(clockid_t clock, struct __kernel_timespec *res) > { > int ret = __cvdso_clock_getres_common(clock, res); > > if (unlikely(ret)) > return clock_getres_fallback(clock, res); > return 0; > } > > When the return code of the "vdso" internal function returns an error the system > call is triggered. But when __cvdso_clock_getres_common() does *not* return an error, it means that it handled the clock_getres() call without a fallback to the syscall. I assume this is possible on arm32. When the clock_getres() is handled directly (not as a syscall), why doesn't arm32 need the same (res >= TASK_SIZE) check? > In general arm32 has been ported to the unified vDSO library hence it has a > proper implementation on par with all the other architectures supported by the > unified library. And that's what I do not fully understand. When the call doesn't fall back to a syscall, why does arm32 and arm64 compat need to differ in the implementation? I may be missing something here. > >>> My guess is that on arm32 it only fails with -EFAULT in the syscall > >>> fallback path since a copy_to_user() would fail the access_ok() check. > >>> Does it always take the fallback path if ts > TASK_SIZE? > >> > >> Correct, it goes via fallback. The return codes for these syscalls are specified > >> by the ABI [1]. Then I agree with you the way on which arm32 achieves it should > >> be via access_ok() check. > > > > "it should be" or "it is" on arm32? [...] > SYSCALL_DEFINE2(clock_gettime, const clockid_t, which_clock, > struct __kernel_timespec __user *, tp) [...] > This is the syscall on which we fallback when the "vdso" internal function > returns an error. The behavior of the vdso has to be exactly the same of the > syscall otherwise we end up in an ABI breakage. I agree. I just don't understand why on arm32 the vdso code doesn't need to check for tp >= TASK_SIZE while the arm64 compat one does when it does *not* fall back to a syscall. I understand the syscall fallback case, that's caused by how we handle access_ok(), but this doesn't explain the vdso-only case. > >>>>> This last check needs an explanation. If the clock_id is invalid but res > >>>>> is not NULL, we allow it. I don't see where the compatibility issue is, > >>>>> arm32 doesn't have such check. > >>>> > >>>> The case that you are describing has to return -EPERM per ABI spec. This case > >>>> has to return -EINVAL. > >>>> > >>>> The first case is taken care from the generic code. But if we don't do this > >>>> check before on arm64 compat we end up returning the wrong error code. > >>> > >>> I guess I have the same question as above. Where does the arm32 code > >>> return -EINVAL for that case? Did it work correctly before you removed > >>> the TASK_SIZE_32 check? > >> > >> I repeated the test and seems that it was failing even before I removed > >> TASK_SIZE_32. For reasons I can't explain I did not catch it before. > >> > >> The getres syscall should return -EINVAL in the cases specified in [1]. > > > > It states 'clk_id specified is not supported on this system'. Fair > > enough but it doesn't say that it returns -EINVAL only if res == NULL. > > Actually it does, the description of getres() starts with: > > 'The function clock_getres() finds the resolution (precision) of the > specified clock clk_id, and, if res is *non-NULL*, stores it in the > struct timespec pointed to by res.' > > Please refer to the system call below of which we mimic the behavior in the vdso > (kernel/time/posix-timers.c): > > SYSCALL_DEFINE2(clock_getres_time32, clockid_t, which_clock, > struct old_timespec32 __user *, tp) > { > const struct k_clock *kc = clockid_to_kclock(which_clock); > struct timespec64 ts; > int err; > > if (!kc) > return -EINVAL; > > err = kc->clock_getres(which_clock, &ts); > if (!err && tp && put_old_timespec32(&ts, tp)) > return -EFAULT; > > return err; > } > > If the clock is bogus and res == NULL we are supposed to return -EINVAL and not > -EFAULT or something else. If the clock is bogus, the above returns 'err' irrespective of the value of 'tp'. I presume 'err' is -EINVAL in this case. But there is no condition that tp == NULL above. What the above tries to achieve is that if there is no error (err == 0) and tp != NULL, try to write the timespec to the user tp pointer. If put_old_timespec32() fails, that's when we return -EFAULT. > This is what the test is trying to verify. If the check below is not > in place on arm64 compat, I get error report from the test suite. > if (!VALID_CLOCK_ID(clock_id) && res == NULL) > return -EINVAL; I really don't get where you deduced that you need to check for res == NULL. The above should be: if (!VALID_CLOCK_ID(clock_id)) return -EINVAL; Furthermore, my assumption is that __cvdso_clock_getres_common() should handle this case already and we don't need it in the arch vdso code. > > You also don't explain why __cvdso_clock_getres_time32() doesn't already > > detect an invalid clk_id on arm64 compat (but does it on arm32). > > > > Thanks for asking to me this question, if I would not have spent the day trying > to explain it, I would not have found a bug in the getres() fallback: > > diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h > index 1dd22da1c3a9..803039d504de 100644 > --- a/arch/arm64/include/asm/unistd.h > +++ b/arch/arm64/include/asm/unistd.h > @@ -25,8 +25,8 @@ > #define __NR_compat_gettimeofday 78 > #define __NR_compat_sigreturn 119 > #define __NR_compat_rt_sigreturn 173 > -#define __NR_compat_clock_getres 247 > #define __NR_compat_clock_gettime 263 > +#define __NR_compat_clock_getres 264 > #define __NR_compat_clock_gettime64 403 > #define __NR_compat_clock_getres_time64 406 > > In particular compat getres is mis-numbered and that is what causes the issue. > > I am going to add a patch to my v5 that addresses the issue (or probably a > separate one and cc stable since it fixes a bug) and in this patch I will remove > the check on VALID_CLOCK_ID. Please send this as a separate patch that should be merged as a fix, cc stable. > I hope that this long email helps you to have a clearer picture of what is going > on. Please let me know if there is still something missing. Not entirely. Sorry. -- Catalin